Electrical connection of components

ABSTRACT

A component is electrically connected to an electrical circuit by a method that comprises forming an intermediate product in which the component ( 3 ) is disposed on one side of an electrically conducting sheet ( 1 ) so that at least one pair of contacts ( 4 ) of the component are electrically connected by the sheet and in which a patterned etch resist layer ( 2 ) is disposed on the other side of the sheet in registration with the component on said one side of the sheet, and then exposing the other side of the sheet to an etching agent and thereby removing areas of the sheet to leave the electrical circuit and also to remove the electrical interconnection between the contacts.

This application is a 371 filing of PCT/GB2008/000935 (WO 2008/113994),filed Mar. 17, 2008, claiming priority benefit of GB 0705287.1, filedMar. 20, 2007 and U.S. Provisional Patent Application No. 60/918,913,filed Mar. 20, 2007.

FIELD OF THE INVENTION

This invention relates to a method of electrically connecting acomponent to an electrical circuit, and to the resulting circuitry. Theinvention has particular, but not exclusive, application to themanufacture of cards for RFID (radio frequency identification devices)and IC cards, so called smart cards, where a component such as anintegrated circuit is attached to an antenna or other electricallyconductive element.

BACKGROUND TO THE INVENTION

The basic components of an RFID chip or tag for an RFID card comprise asubstrate (usually a plastic film or paper), a patterned conductiveantenna and an integrated circuit which may store data and beinterrogated. The RFID industry is mainly driven by cost and significantadvances have been made in reducing the cost of the chips which are usedin RFID. A significant amount of work has also occurred in bringing downthe cost of the antenna. The utilisation of additive metallizationmethods, printing and low-cost materials have all contributed to areduction in the cost of antenna production. However, a significant costin the manufacture of the RFID card still comes from the process ofattaching the chip to the antenna. As well as the need to form aconductive bond between the chip and antenna, the precision with whichthe chip must be placed requires expensive and relatively slowequipment.

RFID antennas and other electrical conductive elements are traditionallymanufactured by a process of masking and etching metal-coveredsubstrates. For example, a plastic or composite substrate (e.g. PET orFR4 epoxy composite) is co-laminated with a copper or aluminium foil.The metal structure would then be coated and patterned with an etchresistant material (e.g. photoresist) and then immersed in a chemicaletchant (ferric chloride, nitric acid or a mixture of peroxide andsulphuric acid in the case of copper, hydrochloric acid or sodiumhydroxide in the case of aluminium) to remove the excess metal foil. Theetch resist would then be removed to leave a patterned metal layer inthe form of an antenna. The RFID inlay would then be completed byattaching an RFID chip to the antenna such that raised contact bumps onthe surface of the chip come into electrical contact with contact padsat the feed points of the antenna. This may be done by first connectingthese bumps to a larger metal structure (known as a strap or interposer)which is then bonded to the antenna, or by directly placing the chipface down on the antenna with the contact bumps on top of the contactpads. In either case, good electrical contact and mechanical bonding areachieved by the use of a conductive adhesive paste or film. In manycases this adhesive is anisotropically conductive (i.e. the conductivityin the lateral or in-plane direction is much lower than that in thevertical direction) so as to prevent shorting between the bumps.

In an alternative approach the antenna itself may be fabricated using anadditive patterning technique. Under this methodology the conductiveregion is added patternwise (usually using a printing technique) to theinsulating substrate. This may be done by printing a paste or suspensionof metal particles such as silver or copper. Alternatively it may beachieved by printing a catalytic material which is then coated withmetal using a process of electroless deposition. In either case theantenna conductivity may be further increased by subsequent electrolyticplating.

In the above cases, the conducting materials in their chosen form areusually found to be far more costly than simple metal foils. Inparticular, aluminium foil is particularly abundant and available atsignificantly lower cost (per unit area) than the materials usually usedfor antenna manufacture. Consequently, some manufacturers choose todirectly die-cut aluminium foil to form antennas. This method, althoughcheap, greatly limits the complexity of the antennas which may be formedand leads to great difficulties in the handling of the materials duringsubsequent processes.

In addition to the cost of the antenna, the cost of accurately locatingthe bumped pads of the chips to the contacts on the antenna is alsosignificant (in terms of process time and the capital equipmentinvolved).

As an alternative approach, the applicants have demonstrated (e.g. in WO2005/044451) the ability to place the chip relatively inaccurately withthe contact pads facing upwards, and utilise the digital nature ofinkjet printing to print the connection between the antenna and thecontact bumps. Even so, this process still requires the fabrication ofan antenna by either a traditional additive or subtractive method. Theinvention employs a different way of ensuring that there is accurateregistration between the component and the electrical circuit to whichit is to be electrically connected.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of electricallyconnecting a component to an electrical circuit, the method comprisingforming an intermediate product in which the component is disposed onone side of an electrically conducting sheet so that at least one pairof contacts of the component are electrically connected by the sheet andin which a patterned etch resist layer is disposed on the other side ofthe sheet in registration with the component on said one side of thesheet, and then exposing the other side of the sheet to an etching agentand thereby removing areas of the sheet to leave the electrical circuitand also to remove the electrical interconnection between the contacts.

Thus, in the inventive method the component is disposed on said one sideof the sheet and the etch resist layer accurately positioned on theother side, before the etching step takes place. The etch resist layermay be disposed on the other side of the sheet by a digital printingprocess, such as inkjet printing.

Preferably, the patterned etch resist layer is applied to the other sideof the sheet in the required registration by an optical system whichlocates the position at which the component is disposed on the said oneside of the sheet. The optical system may locate indentations in thesheet produced by contact bumps on the component. This allows for thecomponent to be disposed on said one side of the sheet relativelyinaccurately because the optical system accurately positions thepatterned etch resist layer with respect to the component.

In one preferred method the intermediate product is formed by applyingthe patterned etch resist layer to the other side of the sheet and thendisposing the component on said one side of the sheet.

In an alternative method, the intermediate product is formed bydisposing the component on said one side of the sheet and then applyingthe patterned etch resist layer to the other side of the sheet.

The intermediate product may be formed by applying a further etch resistlayer to said one side of the sheet and to the exposed surface of thecomponent, and in this case the further etch resist layer may be appliedto the one side of the sheet wholly or substantially covering the oneside of the sheet so as to form a substrate.

The further etch resist layer applied to said one side of the sheet mayhave a pattern and may be exposed to a corresponding etching agent whichremoves areas of the sheet not covered by the etch resist layer on saidone side of the sheet, whereby the electrical circuit is defined bypathways formed by etching from both sides of the sheet. In this casethe etch resist layers may be made of the same etch resistant materialand may be subjected simultaneously to the same etching agent, forexample by dipping into the etching agent.

The component may be an integrated circuit chip but may also be aresistor, inductor, or capacitor which could be printed directly ontothe sheet. The sheet may be made of any electrically conductivematerial, metal or non-metal, but is preferably aluminium foil becausethis is inexpensive and available in a readily useable form.

BRIEF DESCRIPTION OF THE DRAWINGS

Methods according to the invention, and the products obtained therefrom,will now be described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1, consisting of FIGS. 1 a to 1 f, illustrates a first method,

FIG. 2, consisting of FIGS. 2 a to 2 e, illustrates a second method,

FIG. 3, consisting of FIGS. 3 a to 3 e, illustrates a third method,

FIG. 4, consisting of FIGS. 4 a to 4 e, illustrates a fourth method,

FIG. 5, consisting of FIGS. 5 a to 5 e, illustrates a fifth method,

FIG. 6, consisting of FIGS. 6 a to 6 d, illustrates a sixth method,

FIG. 7, consisting of FIGS. 7 a to 7 d, illustrates a seventh method,

FIG. 8, consisting of FIGS. 8 a to 8 d, illustrates a eighth method,

FIG. 9, consisting of FIGS. 9 a to 9 e, illustrates an ninth method,

FIG. 10, consisting of FIGS. 10 a to 10 c, illustrates a tenth method,

FIG. 11, consisting of FIGS. 11 a to 11 f, illustrates a eleventhmethod, and

FIGS. 12 and 13 illustrate how camera systems can be used for alignmentpurposes in the described methods.

DETAILED DESCRIPTION OF THE DRAWINGS

Throughout the drawings corresponding parts bear the same referencenumerals.

Referring to FIG. 1, a continuous electrically conducting sheet in theform of a metal foil 1 has applied to a surface a patterned etch resistlayer 2 defining an electrical circuit to be formed. A component in theform of a chip 3 with spaced contact pads 4 is placed on the oppositeside of the foil 1 such that the contact pads 4 make electrical contactwith the foil 1 and register with the areas of the etch resist layer 2.The component side of the foil 1 is completely coated with a second etchresist layer 5 which fills the region 6 between the pads 4 and thusforms an underfill.

The resulting intermediate product of FIG. 1 d is then immersed in achemical or other etch solution which dissolves the unprotected areas offoil so as to leave conductive regions 1′ of the foil corresponding tothe areas covered by the etch resist layer 2. Also, this etching processremoves the metal foil between the contact pads 4 and thus breaks theelectrical contact between the pads 4, as shown by the discontinuity 7in the foil (FIGS. 1 e and 1 f). The etch resist layer 2 may be left inplace to form a substrate for the resulting device, or it may bestripped away (FIG. 1 f).

The application of the etch resist layer 2 may be performed patternwiseby a process such as analogue or digital printing (e.g. screen, flexo,gravure, inkjet printing or laser printing). Alternatively, the maskrepresented by the layer 2 may be applied by a traditional photolithographic method such as the application of a photo resist (dry filmor liquid), subsequent exposure to light through a mask, followed by adeveloping stage.

Also, the chip 3 may be secured to the metal foil 1 by using an adhesivewhich may be cured or allowed to set. Alternatively, the second etchresist layer 5 may be used to completely flow around the chip and bondit to the substrate.

A chemical etch material may be used to remove unprotected metal.Alternatively other etching processes such as electrochemical or plasmaetching may also be used. In the case of plasma etching the process maybe non-directional or directional, such as reactive ion etching.

FIG. 2 differs from FIG. 1 in that the chip 3 is first placed in contactwith one surface of the metal foil 1, and the patterned etch resistantlayer 2 then applied to the other side of the foil. In common with FIG.1, the chip side is then completely coated with a second etch resistlayer 5 to form the intermediate product (FIG. 2 c) identical to that ofFIG. 1 d. The resulting product is then etched, FIG. 2 d, and the etchresist layer 2 may then be stripped away, as shown in FIG. 2 e.

FIG. 3 shows a variation of the method of FIG. 2. In FIG. 3, the layer 2has several strips (FIG. 3 b) so the intermediate product appears asillustrated in FIG. 3 c. After etching, there are a plurality ofdiscontinuities 7 between the separated pathways which then correspondto the strips of the layer 2, as shown in FIG. 3 d. If the layer 2 isstripped away, the result is as shown in FIG. 3 e. The method of FIG. 3is especially relevant to HF (13.56 MHz) RFID tags where the tag isusually in the form of a spiral and one of the major manufacturingproblems is making a connection from the inside of the spiral to theoutside without shorting the tracks in between. A chip on an interposercould be used to bridge the gap. An insulating adhesive may also be usedso as to insulate from the intermediate tracks. Failing that a metalstrip with an insulating coating under it could also be used to bridgethe gap.

In FIG. 4 the chip 3 is first placed on the metal foil 1 (FIG. 4 a)after which the etch resist layer 5 is coated over the chip side of thefoil (FIG. 4 b). The patterned etch resist layer 2 is then applied tothe opposite side of the foil (FIG. 4 c) to form the intermediateproduct which is then etched (FIG. 4 d), after which the patterned etchresist layer 2 may be stripped (FIG. 4 e).

Referring to FIG. 5, the chip 3 is adhered to the metal foil 1 (FIG. 5a) using an adhesive material 8. The layer 2 is then applied (FIG. 5 b).The material 8 may or may not be used as an etch resistant materialwhich ensures that the area between the contact pads is completelyfilled. FIG. 5 c represents the intermediate product which is thensubjected to etching, FIG. 5 d, and then optional stripping of thepatterned etch resist layer 2, as shown in FIG. 5 e.

The variation shown in FIG. 6 uses a conductive material 9 for adheringthe chip pads 4 to the metal foil 1. The conductive material 9 may be anelectrically conductive paste or glue, solder or other electricallyconductive material. The etch resist layer 2 is then applied to theopposite side of the foil, as shown in FIG. 6 b, and after this thefurther etch resist layer 5 is applied to the chip side of the foil soas to cover the foil and the exposed areas of the chip. This results inthe intermediate product shown in FIG. 6 c where it can be seen that thematerial forming the etch resist layer 5 has flowed under the chip bycapillary action and thus acts as an underfill. The intermediate productof FIG. 6 c is then etched, as previously described, the result beingillustrated in FIG. 6 d.

In the method illustrated in FIG. 7, the chip 3 is adhered to the foil 1using an anisotropic conductive paste or an anisotropic conductive film10. This is a material which comprises a binder layer and sparselydistributed conductive particles such that when the chip 3 is pressedinto the film or paste 10 the particles are pressed together to make thefilm or paste conductive only in the vertical direction, or thedirection of compression. This has the advantage that it ensures goodelectrical connection to the foil without causing short circuit betweenthe contact pads 4. After the chip has been adhered in this way, thepatterned etch resist layer 2 is then applied (FIG. 7 b) and the secondetch resist layer 5 is applied (FIG. 7 c). This intermediate product isthen etched to produce the product shown in FIG. 7 d.

FIGS. 8 a and 8 b correspond to FIGS. 2 a and 2 b. FIG. 8 c shows how aplurality of chips 3 can be placed on the foil 1 to provide a pluralityof devices. A second etch resist layer 12 is then applied, FIG. 8 c,after which etching proceeds to give the result illustrated in FIG. 8 d.

It will be appreciated that the second etch resist layer 12 may beformed by a lamination process or by the deposition of a liquid which isthen solidified or allowed to solidify. Also, the second etch resistmaterial may be applied as a continuous layer or may be applied patternwise such that the device substrates are also patterned or partially orfully singulated after the etching process.

FIGS. 9 a and 9 b respectively correspond to FIGS. 8 a and 8 b. FIG. 9 cshows the second etch resist layer applied to the chip side of the foiland acting as an underfill, and FIG. 9 d illustrates how a further etchresist layer 12 may be laminated onto the structure, after which etchingtakes place to produce the result shown in FIG. 9 e.

FIG. 10 illustrates how certain contact pads 13 of the chip 3 areinitially short circuited by the foil 1 and deliberately remain shortcircuited even after the etching process, as illustrated by FIG. 10 c.The chip also has pads which are electrically isolated by the etchingprocess, as in the preceding methods, and one such pad may be one of thepads 13.

FIGS. 11 a to 11 c correspond to FIGS. 4 a to 4 c respectively, but itwill be noted in FIG. 11 c that the etch resist layer 2 has furtherpathways so that after etching and stripping of the layer 2 one or moreadditional components 14 may be applied to the metal foil, thusproviding a method of populating both sides of the metal foil withcomponents, i.e. producing a buried component board.

It will be appreciated that in addition to placing semiconductor devicesand other components, components such as resistors, inductors orcapacitors can be printed directly onto the foil. This applies to eachof the foregoing examples. By the use of printable semiconductors (suchas conjugated polymers), active components such as thin filmtransistors, LEDs or memory elements can also be printed.

In the production of the intermediate product in the foregoing examples,the chip 3 and layer 2 are disposed on the foil 1 in accurateregistration by an optical system, for example as shown in FIG. 12 or13.

Referring to FIG. 12, two cameras 15 may be disposed on respective sidesof a transparent platform 16. A calibration pattern 17 on a transparentsubstrate 18 is used to ensure that both cameras 15 see an identicalview (in terms of magnification and field of view) of the resistpattern. Computer software may then be used to superimpose the imagesfrom the two cameras 15 such that the detail of both sides of thecalibration pattern are visible on the same image at the same time. Theimage from one of the cameras must be mirrored about one axis in orderto achieve this and this is an option with the available software. Whena patterned opaque substrate is then placed on the transparent platformwith the pattern facing the lower camera, this vision system may then beused to place a component on the upper side of the substrate in registerwith the pattern on the underside.

Referring to FIG. 13, the same camera system may be used to align aphoto mask 19 with a photo resist layer in the situation where the chip3 has been previously placed on a metal foil 1. Although this systemdescribes the procedure for placing components or aligning patterns byhand, it will be appreciated that machine vision technology couldreadily be used to automate such a system, i.e. such that componentscould be automatically placed relative to a pattern or such that apattern could be formed (either by printing or lithographic means) inregister with a pre-placed device. In particular, the process of digitalprinting (e.g. inkjet printing, laser printing or laser direct imaging)could be used to print features or connections between components suchthat the positions of the components are used as the input to a computerprogramme which then generates the correct image to be printed in orderto connect the components.

The three following formulations have been found to be suitable for theink used for the etch resistant material, where the foil is aluminiumfoil.

Formulation 1

This is a modification of the applicants' base ink in order to improvemetal adhesion as well as resistance to acids.

Materials % DPGDA^(i) 43.7 CN 2505^(ii) 5.5 DPHA^(iii) 3.3 SR 9003^(iv)26.2 SR 9050^(v) 15.0 Irgacure 819^(vi) 2 Irgacure 127^(vi) 4.3Viscosity@25° C. 23.3 cpsFormulation 2

A modification of Formulation 1 with an aim to increase hydophobicity byincorporating more non-polar acrylates (HDDA and IBOA) in place of DPGDAand SR9003. Also reduces viscosity.

Materials % HDDA^(vii) 42.5 CN 2505 6.6 DPHA 4.1 IBOA^(viii) 25.5 SR9050 15.0 Irgacure 819 2.0 Irgacure 127 4.3 Viscosity@25° C. 15.1 cpsFormulation 3

Formulation 2 gave a slightly brittle film and a low viscosity fluid andso was modified with more oligomer (at the expense of the brittle IBOA)

Materials % HDDA 42.5 CN 2505 12.6 DPHA 8 IBOA 15.6 SR 9050 15.0Irgacure 819 2.0 Irgacure 127 4.3 Viscosity @ 25° C. 15.1 cps^(i)Dipropyleneglycol diacrylate - supplied by Cytec SurfaceSpecialities ^(ii)Tetrafunctional polyester acrylate oligomer - suppliedby Sartomer ^(iii)Dipentaerythritol hexaacrylate - supplied by CytecSurface Specialities ^(iv)Neopentylglycol diacrylate - supplied bySartomer ^(v)Acid functional oligomer - supplied by Sartomer^(vi)Photoinitiator - supplied by Ciba Speciality Chemicals^(vii)Hexanediol diacrylate - supplied by Cytec Surface Specialities^(viii)Isobornyl acrylate - supplied by Cytec Surface Specialities

Two examples of detailed methods follow:

Example 1

Inkjet printing is used (using two XaarJet 500/40 industrial inkjetprintheads and associated drive electronics) to deposit the resistdescribed in Formulation 3 onto a 10 micron thick copper foil. The imageis then cured by passing it under a Light Hammer 6 UV lamp from FusionSystems.

The image is deposited in the form of an antenna for Wireless Local AreaNetwork communication at 2.45 GHz. The antenna is formed of multipleisolated areas, so arranged such that surface mount capacitors andinductors may be placed on the pattern, bridging the gaps between theisolated areas.

Two capacitors and an inductor are prepared for mounting by applying asmall amount of a conductive epoxy resin (from ITW Chemtronics) on thecontact pads at each end of each device. An insulating epoxy resin(Araldite Rapide—from Huntsman) is applied to each component, betweenthe contact pads—this serves to further secure the device to thesubstrate but also to provide an insulating sealed region between thecontact pads.

The imaging system described in FIG. 12 is used to place the capacitorsand inductor onto the reverse side of the metal foil such that theybridge the gaps in the printed resist pattern. The adhesives are thencured in an oven at 60° C. for 2 hours.

A further layer of epoxy resin is then applied across the whole of thecomponent side of the foil. A layer of Melinex 339 PET film (from DuPontTeijin Films) is then laminated onto the epoxy. The whole device is thenallowed to cure in the oven at 60° C. for a further 4 hours.

The cured structure is then immersed in a solution of 10% sulphuric acidand 5% potassium persulfate at 50° C. until all the copper foil betweenthe areas of resist has been etched away. A Clincher connector (FromFCI) is then used to pierce the whole device structure and make externalcontact to the antenna for connection to the rest of the circuit.

Example 2

A UHF RFID chip from Texas Instruments was bonded to a 12 μm thickaluminium foil using and anisotropic conductive film IOB-3 fromBetchcorp, Colo. The chip was pressed into the film using a pressure of25 psi, on a hotplate at 50° C. and held in place for 5 seconds. Theassembled device was then cured in an oven at 130° C. for 1 hour.

The device was then placed chip-side-down on the sample stage of aDMP-2831 inkjet print system from Dimatix. The DMP-2831 system includesan integrated fiducial recognition camera which was then used to findthe indentations produced in the aluminium foil by the contact bumps onthe chip. The alignment software included with the DMP-2831 was thenused to print the image of a UHF RFID antenna such that the contactpoint of the antenna lined up with the indentations of the contactbumps. The image was printed using the resist formulation describedabove as Formulation 3. The resist was cured during the print processusing the output fibre of a fibre coupled UV lamp (Exfo) which wasretrofitted to the cartridge mount of the DMP-2831.

A Xaar Jet 500/80 print head was then used to print a complete coveringof the same resist ink on the reverse (chip) side of the aluminium foil.This was cured using a Light hammer 6 UV lamp from Fusion Systems.

The excess metal was then etched away using a 10% solution ofhydrochloric acid.

The result was a self supporting working RFID tag.

1. A method of electrically connecting a component to an electricalcircuit, the method comprising forming an intermediate product in whichthe component is disposed on one side of an electrically conductingsheet so that at least one pair of contacts of the component areelectrically connected by the sheet and in which a patterned etch resistlayer is disposed on the other side of the sheet in registration withthe component on said one side of the sheet, applying a further etchresist layer to said one side of the sheet and to the exposed surface ofthe component, and then exposing the other side of the sheet to anetching agent and thereby removing areas of the sheet to leave theelectrical circuit and also to remove the electrical interconnectionbetween the contacts.
 2. A method according to claim 1, wherein thepatterned etch resist layer is applied to the other side of the sheet inthe required registration by an optical system which locates theposition at which the component is disposed on the sheet.
 3. A methodaccording to claim 2, wherein the optical system locates indentations inthe sheet produced by contact bumps on the component.
 4. A methodaccording to claim 3, wherein the etch resist layer is disposed on theother side of the sheet by a digital printing process.
 5. A methodaccording to claim 4, wherein the optical system employs two cameras onrespective sides of the sheet to achieve said required registration. 6.A method according to claim 5, wherein the intermediate product isformed by applying the patterned etch resist layer to the other side ofthe sheet and then disposing the component on the one side of the sheet.7. A method according to claim 5, wherein the intermediate product isformed by disposing the component on said one side of the sheet and thenapplying the patterned etch resist layer to the other side of the sheet.8. A method according to claim 1, wherein the further etch resist layerapplied to the one side of the sheet wholly or substantially whollycovers the one side of the sheet and thereby forms a substrate.
 9. Amethod according to claim 1, wherein the further etch resist layerapplied to the one side of the sheet has a pattern and is exposed to acorresponding etching agent which removes areas of the sheet not coveredby the etch resist layer on the one side of the sheet, whereby theelectrical circuit is defined by pathways formed by etching from bothsides of the sheet.
 10. A method according to any claim 9, wherein theetch resist layers are made of the same etch resistant material and aresubjected simultaneously to the same etching agent.
 11. A methodaccording to claim 1, wherein the further etch resistant layer flowsbetween the chip and the sheet to act as an underfill material.
 12. Amethod according to claim 1, wherein the patterned etch resist layer isremoved after etching by the etching agent.
 13. A method according toclaim 1, wherein the patterned etch resist layer remains in place toform a protective layer for the electrical circuit.
 14. A methodaccording to claim 1, wherein the component is adhered to the one sideof the sheet by means of an adhesive material.
 15. A method according toclaim 14, wherein the adhesive material acts as an etch resist materialthat ensures that the region between the pair of contacts is filled. 16.A method according to claim 1, wherein the intermediate product isformed by adhering the component to said one side of the sheet by ananisotropic conductive material which provides electrical connectionbetween each contact and the sheet without causing an electrical shortcircuit between the pair of contacts through the anisotropic material.17. A method according to claim 1, wherein the intermediate product hasa plurality of components disposed on said one side of the sheet and theetch resist layer disposed on the other side of the sheet defineselectrical pathways forming the electrical circuit in register with thecomponents.
 18. A method according to claim 1, wherein the component isan integrated circuit chip.
 19. A method according to claim 1, whereinthe foil is aluminum foil.
 20. A method according to claim 1, wherein atleast one additional component is disposed on the other surface of thesheet.
 21. A component connected to an electrical circuit by a methodaccording to claim 1.